Wal-Mart Stores Inc., facing pressure from critics who call its employee health-care coverage inadequate, plans to begin selling nearly 300 generic prescription drugs to its employees and customers at much reduced prices, the company announced yesterday.

The world’s biggest retailer said that it will test the program in Florida that will make 291 generic drugs available — which are used to treat a variety of condition from allergies to high-blood pressure — for only $4 a prescription for up to a 30-day supply. It also will be available to the uninsured.

The program will be launched on Friday at 65 Wal-Mart, Neighborhood Market, and Sams’ Club pharmacies in the Tampa Bay area in Florida and will be expanded to the entire state in January.

The company said it plans to take the program to as many states as possible next year.

On average, generic drugs cost between $10 and $30 for a 30-day prescription.

“Each day in our pharmacies we see customers struggle with the cost of prescription drugs,” the CEO of Wal-Mart, H. Lee Scott, Jr., said in a statement. “By cutting the cost of many generics to $4, we are helping to ensure that our customers and associates get the medicines they need at a price they can afford.”

The initiative would be the fourth time since last October that Wal-Mart has moved to improve health benefits.

Wal-Mart’s recent moves to improve its health care plan include relaxing eligibility requirements for its part-time employees who want health insurance and extending coverage for the first time to the children of those employees. Part-time employees, who had to work for Wal-Mart for two years to qualify, now have to work at the company for one year. This year, Wal-Mart also expanded a trial run of in-store clinics, aimed at providing lower cost nonemergency health-care to the public.

Last October, Wal-Mart offered a new lower-premium insurance aimed at getting more of its work force on company plans.

But critics argue that Wal-Mart’s coverage calls for a deductible that requires workers to pick up the first $1,000 in medical expenses, and the deductible rises to a maximum of $3,000 for families.

Union-backed Wake Up Wal-Mart, one of its most vociferous critics, has called upon Bentonville, Ark.-based Wal-Mart to offer better health-care coverage and higher pay to employees.

Critics contend that the company’s benefits are too stingy, forcing taxpayers to absorb more of the cost as the workers lacking coverage turn to statefunded health care programs.

This past summer, Wal-Mart won a successful fight against a first-of-its-kind state law that would have required the retailer to spend more on employee health-care in Maryland. A federal judge ruled in July that it was invalid under federal law. But other states are considering similar legislation aimed at the company.